1. Field of the Invention
The present invention relates to apparatus and methods for twisting one coaxial lumen relative to the other. The present invention also relates to a medical apparatus tip for over-the-guidewire intravenous insertion of the apparatus. More particularly, the present invention is directed to apparatus and methods for furling and introducing an extrapulmonary blood gas exchange device in order to perform extrapulmonary blood gas exchange.
2. Technology Review
Thousands of patients in hospitals suffer from inadequate blood gas exchange, which includes both inadequate blood oxygenation and inadequate removal of carbon dioxide (CO.sub.2). These conditions are commonly caused by varying degrees of respiratory inadequacy usually associated with acute lung illnesses such as pneumonitis, atelectasis, fluid in the lung, or obstruction of pulmonary ventilation. Various heart and circulatory aliments such as heart disease and shock can adversely affect the flow of blood and thereby also reduce the rate of blood gas exchange.
Currently the most widely used methods of treating these types of blood gas exchange inadequacies involve increasing the flow of oxygen through the lungs by either increasing the oxygen concentration of the inspired gases or by mechanically ventilating the lungs. Both methods result in placing further strain on the lungs, which may be diseased and unable to function at full capacity. In order to allow diseased or injured organs to heal it is generally best to allow these organs a period of rest followed by a gradual increase in activity. The current methods of treating inadequate blood gas exchange, however, force the diseased or damaged lungs to work even harder rather than allowing them a period of rest and recovery.
Various devices have been developed which are capable, at least for a limited period of time, of taking over the gas exchange function of the lungs. Many extracorporeal blood oxygenators are in common use and are employed most frequently during heart surgery. These devices are capable of providing blood oxygenation sufficient to carry the patient through the surgical procedure. These oxygenators include devices which bubble oxygen into the blood as the blood flows through the device. This is usually followed by a section of the device which defoams the blood to make it acceptable for reinjection into the patient.
Another group of extracorporeal oxygenators employ gas permeable membranes. These devices take many different shapes and configurations; however, the basic concept of operation is the same in all of these devices. Blood flows on one side of the gas permeable membranes while an oxygen rich gas flows on the other side of the membrane. As the blood flows through the device, the oxygen travels across the gas permeable membrane and enters the blood. This allows oxygenation of the blood without actually introducing oxygen bubbles into the blood and without the corresponding need for an extensive defoaming apparatus.
Gas permeable membranes used in such extracorporeal oxygenators are of two types. One type uses a microporous membrane which allows blood gas interface through micropores in the membrane. The other type is a continuous membrane which does not have micropores but which allows blood gas exchange through the membrane without the blood gas interface.
The microporous and bubble oxygenators discussed above are not suited for use outside the setting of a cardiopulmonary bypass procedure, and are thus typically designed for short term extracorporeal use. As a result, these devices are of limited use in the long term intensive care of respiratory failure patients.
In vivo extrapulmonary blood gas exchange has been demonstrated in the art. One known device, described in U.S. Pat. No. 4,850,958 which is incorporated herein by specific reference, consists of a plurality of elongated gas permeable tubes being bound at each end and enclosed within a respective air tight proximal and distal chamber. A dual lumen tube having an outer lumen and an inner lumen is situated relative to the gas permeable tubes such that the outer lumen terminates within the proximal chamber and such that the inner lumen terminates within the distal chamber.
The overall, outside diameter of the bundle of gas permeable tubes is selectively adjusted to provide either a furled, small insertion diameter when inserting the apparatus into the venae cavae of a patient or an unfurled, expanded oxygenation diameter after the apparatus is in place within the venae cavae and the bundle of gas permeable tubes is deployed therein. One of either the inner and outer lumens are connected to a source of oxygen rich gas. The other lumen is connected to an exhaust tube or other means for allowing the gas to flow out of the device.
U.S. Pat. No. 4,850,958 describes a device and method for furling the bundle of gas permeable tubes. The distal chamber is twisted relative to the proximal chamber by means of a stylet which passes through the inner lumen and engages the distal end of the inner lumen. Because the inner lumen is nonrotatably secured to the distal chamber, twisting the stylet simultaneously twists the distal chamber. Thus, by twisting the stylet relative to the proximal chamber, the distal chamber is twisted, thereby twisting the bundle of gas permeable tubes.
While the method of inserting this extrapulmonary blood gas exchange device within a patient's venae cavae has been successfully demonstrated, still there are some drawbacks. First, the need for a stylet which engages the distal end of the inner lumen in order to place the apparatus in a furled, insertion diameter means that the stylet must be fully inserted within the inner lumen during insertion. When the stylet extends fully to the distal end of the inner lumen, the flexibility of the distal end is substantially reduced. In practice, a rigid distal end is more difficult to insert through the patient's winding vascular system and is more likely to cause trauma to the sensitive intimal tissues of the patient's venous system.
Second, the furling device described in U.S. Pat. No. 4,850,958 did not provide any mechanism for indicating when the apparatus was fully furled and for preventing excessive furling. It has been found that the gas permeable tubes may be damaged by over-twisting.
Another significant drawback with the described furling device is the risk of sudden and undesired unwinding, for example, during insertion. If the stylet were accidentally released while the bundle of gas permeable tubes was fully twisted, the bundle would naturally unwind. This is a serious problem if the apparatus is in the process of being inserted into the patient's venae cavae. The risk exists because the screw for securing the stylet is always exposed to potential release during the insertion procedure.
A serious drawback also exists with the current apparatus insertion method. Due to the large size of the apparatus, a guidance system is needed to guide the apparatus through the peripheral venous system into the venae cavae. A common prior art system for introducing catheters and the like within a patient's vascular system is the "over-the-guidewire" technique (sometimes referred to as "OTG"). In this technique, a thin guidewire (typically a "J-tip" spring guidewire) is inserted into the vessel and guided to the desired location. The catheter or other device is then inserted over the guide wire, thereby following the guidewire to the desired location. Once the device is in place, the guidewire is withdrawn.
The OTG insertion technique may only be used with a device that has on open distal end. For this reason, the OTG method has been used primarily for open ended catheters and similar devices. It will be appreciated that the intravenous oxygenation device described in U.S. Pat. No. 4,850,958 does not have an open distal end and therefore could not be used with the OTG insertion method.